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• Socket Read In Multi-Threaded Application Returns Zero Bytes or EINTR (104)

  - by user309670

  Hi. Am a c-coder for a while now - neither a newbie nor an expert. Now, I have a certain daemoned application in C on a PPC Linux. I use PHP's socket_connect as a client to connect to this service locally. The server uses epoll for multiplexing connections via a Unix socket. A user submitted string is parsed for certain characters/words using strstr() and if found, spawns 4 joinable threads to different websites simultaneously. I use socket, connect, write and read, to interact with the said webservers via TCP on their port 80 in each thread. All connections and writes seems successful. Reads to the webserver sockets fail however, with either (A) all 3 threads seem to hang, and only one thread returns -1 and errno is set to 104. The responding thread takes like 10 minutes - an eternity long:-(. *I read somewhere that the 104 (is EINTR?), which in the network context suggests that ...'the connection was reset by peer'; or (B) 0 bytes from 3 threads, and only 1 of the 4 threads actually returns some data. Isn't the socket read/write thread-safe? I use thread-safe (and reentrant) libc functions such as strtok_r, gethostbyname_r, etc. *I doubt that the said webhosts are actually resetting the connection, because when I run a single-threaded standalone (everything else equal) all things works perfectly right, but of course in series not parallel. There's a second problem too (oops), I can't write back to the client who connect to my epoll-ed Unix socket. My daemon application will hang and hog CPU 100% for ever. Yet nothing is written to the clients end. Am sure the client (a very typical PHP socket application) hasn't closed the connection whenever this is happening - no error(s) detected either. Any ideas? I cannot figure-out whatever is wrong even with Valgrind, GDB or much logging. Kindly help where you can.

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• Socket Read In Multi-Threaded Application Returns Zero Bytes or EINTR (-1)

  - by user309670

  Hi. Am a c-coder for a while now - neither a newbie nor an expert. Now, I have a certain daemoned application in C on a PPC Linux. I use PHP's socket_connect as a client to connect to this service locally. The server uses epoll for concurrent connections via a Unix socket. A user submitted string is parsed for certain characters/words using strstr() and if found, spawns 4 joinable threads to different websites simultaneously. I use socket, connect, write and read, to interact with the said webservers via TCP on port 80 in each thread. All connections and writes seems successful. Reads to the webserver sockets fail however, with either (A) all 3 threads seem to hang, and only one thread returns -1 and errno is set to 104. The responding thread takes like 10 minutes - an eternity long:-(. *I read somewhere that the 104 (is EINTR) suggests that ...'the connection was reset by peer', or (B) 0 bytes from 3 threads, and only 1 of the 4 threads actually returns some data. Isn't the socket read/write thread-safe? Otherwise, use thread-safe (and reentrant) libc functions such as strtok_r, gethostbyname_r, etc. *I doubt that the said webhosts are actually resetting the connection, because when I run a single-threaded standalone (everything else equal) all things works perfectly right. There's a second problem too (oops), I can't write back to the client who connect to my epoll-ed Unix socket. My daemon application will hang and hog CPU 100% for ever. Yet nothing is written to the clients end. Am sure the client (a very typical PHP socket application) hasn't closed the connection whenever this is happening - no error(s) detected either. I cannot figure-out whatever is wrong even with Valgrind or GDB

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• Remote Socket Read In Multi-Threaded Application Returns Zero Bytes or EINTR (104)

  - by user39891

  Hi. Am a c-coder for a while now - neither a newbie nor an expert. Now, I have a certain daemoned application in C on a PPC Linux. I use PHP's socket_connect as a client to connect to this service locally. The server uses epoll for multiplexing connections via a Unix socket. A user submitted string is parsed for certain characters/words using strstr() and if found, spawns 4 joinable threads to different websites simultaneously. I use socket, connect, write and read, to interact with the said webservers via TCP on their port 80 in each thread. All connections and writes seems successful. Reads to the webserver sockets fail however, with either (A) all 3 threads seem to hang, and only one thread returns -1 and errno is set to 104. The responding thread takes like 10 minutes - an eternity long:-(. *I read somewhere that the 104 (is EINTR?), which in the network context suggests that ...'the connection was reset by peer'; or (B) 0 bytes from 3 threads, and only 1 of the 4 threads actually returns some data. Isn't the socket read/write thread-safe? I use thread-safe (and reentrant) libc functions such as strtok_r, gethostbyname_r, etc. *I doubt that the said webhosts are actually resetting the connection, because when I run a single-threaded standalone (everything else equal) all things works perfectly right, but of course in series not parallel. There's a second problem too (oops), I can't write back to the client who connect to my epoll-ed Unix socket. My daemon application will hang and hog CPU 100% for ever. Yet nothing is written to the clients end. Am sure the client (a very typical PHP socket application) hasn't closed the connection whenever this is happening - no error(s) detected either. Any ideas? I cannot figure-out whatever is wrong even with Valgrind, GDB or much logging. Kindly help where you can.

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• Interrupted system call during "hg convert"

  - by Aaron Digulla

  When I run "hg convert" to convert a Subversion repository to Mercurial, I get this error: fetching revision log for "/trunk" from 1538 to 0 run hg sink post-conversion action Traceback (most recent call last): File "/usr/lib/pymodules/python2.6/mercurial/dispatch.py", line 46, in _runcatch return _dispatch(ui, args) File "/usr/lib/pymodules/python2.6/mercurial/dispatch.py", line 454, in _dispatch return runcommand(lui, repo, cmd, fullargs, ui, options, d) File "/usr/lib/pymodules/python2.6/mercurial/dispatch.py", line 324, in runcommand ret = _runcommand(ui, options, cmd, d) File "/usr/lib/pymodules/python2.6/mercurial/dispatch.py", line 505, in _runcommand return checkargs() File "/usr/lib/pymodules/python2.6/mercurial/dispatch.py", line 459, in checkargs return cmdfunc() File "/usr/lib/pymodules/python2.6/mercurial/dispatch.py", line 453, in <lambda> d = lambda: util.checksignature(func)(ui, *args, **cmdoptions) File "/usr/lib/pymodules/python2.6/mercurial/util.py", line 386, in check return func(*args, **kwargs) File "/usr/lib/pymodules/python2.6/hgext/convert/__init__.py", line 229, in convert return convcmd.convert(ui, src, dest, revmapfile, **opts) File "/usr/lib/pymodules/python2.6/hgext/convert/convcmd.py", line 398, in convert c.convert(sortmode) File "/usr/lib/pymodules/python2.6/hgext/convert/convcmd.py", line 312, in convert parents = self.walktree(heads) File "/usr/lib/pymodules/python2.6/hgext/convert/convcmd.py", line 109, in walktree commit = self.cachecommit(n) File "/usr/lib/pymodules/python2.6/hgext/convert/convcmd.py", line 267, in cachecommit commit = self.source.getcommit(rev) File "/usr/lib/pymodules/python2.6/hgext/convert/subversion.py", line 433, in getcommit self._fetch_revisions(revnum, stop) File "/usr/lib/pymodules/python2.6/hgext/convert/subversion.py", line 814, in _fetch_revisions for entry in stream: File "/usr/lib/pymodules/python2.6/hgext/convert/subversion.py", line 122, in __iter__ entry = pickle.load(self._stdout) IOError: [Errno 4] Interrupted system call abort: Interrupted system call Apparently, it is possible to restart a read on EINTR but how would I do that with pickle.load()? Also I wonder where that signal comes from? I suspect it's SIGCHILD but shouldn't popen() handle that?

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• Use of select or multithread for almost 80 or more clients?

  - by Tushar Goel

  I am working on one project in which i need to read from 80 or more clients and then write their o/p into a file continuously and then read these new data for another task. My question is what should i use select or multithreading? Also I tried to use multi threading using read/fgets and write/fputs call but as they are blocking calls and one operation can be performed at one time so it is not feasible. Any idea is much appreciated. update 1: I have tried to implement the same using condition variable. I able to achieve this but it is writing and reading one at a time.When another client tried to write then it cannot able to write unless i quit from the 1st thread. I do not understand this. This should work now. What mistake i am doing? Update 2: Thanks all .. I am able to succeeded to get this model implemented using mutex condition variable. updated Code is as below: **header file******* char *mailbox ; pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER ; pthread_cond_t writer = PTHREAD_COND_INITIALIZER; int main(int argc,char *argv[]) { pthread_t t1 , t2; pthread_attr_t attr; int fd, sock , *newfd; struct sockaddr_in cliaddr; socklen_t clilen; void *read_file(); void *update_file(); //making a server socket if((fd=make_server(atoi(argv[1])))==-1) oops("Unable to make server",1) //detaching threads pthread_attr_init(&attr); pthread_attr_setdetachstate(&attr,PTHREAD_CREATE_DETACHED); ///opening thread for reading pthread_create(&t2,&attr,read_file,NULL); while(1) { clilen = sizeof(cliaddr); //accepting request sock=accept(fd,(struct sockaddr *)&cliaddr,&clilen); //error comparison against failire of request and INT if(sock==-1 && errno != EINTR) oops("accept",2) else if ( sock ==-1 && errno == EINTR) oops("Pressed INT",3) newfd = (int *)malloc(sizeof(int)); *newfd = sock; //creating thread per request pthread_create(&t1,&attr,update_file,(void *)newfd); } free(newfd); return 0; } void *read_file(void *m) { pthread_mutex_lock(&lock); while(1) { printf("Waiting for lock.\n"); pthread_cond_wait(&writer,&lock); printf("I am reading here.\n"); printf("%s",mailbox); mailbox = NULL ; pthread_cond_signal(&writer); } } void *update_file(int *m) { int sock = *m; int fs ; int nread; char buffer[BUFSIZ] ; if((fs=open("database.txt",O_RDWR))==-1) oops("Unable to open file",4) while(1) { pthread_mutex_lock(&lock); write(1,"Waiting to get writer lock.\n",29); if(mailbox != NULL) pthread_cond_wait(&writer,&lock); lseek(fs,0,SEEK_END); printf("Reading from socket.\n"); nread=read(sock,buffer,BUFSIZ); printf("Writing in file.\n"); write(fs,buffer,nread); mailbox = buffer ; pthread_cond_signal(&writer); pthread_mutex_unlock(&lock); } close(fs); }

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• Why is this not a bug in qmail?

  - by jemfinch

  I was reading DJB's "Some thoughts on security after ten years of Qmail 1.0" and he listed this function for moving a file descriptor: int fd_move(to,from) int to; int from; { if (to == from) return 0; if (fd_copy(to,from) == -1) return -1; close(from); return 0; } It occurred to me that this code does not check the return value of close, so I read the man page for close(2), and it seems it can fail with EINTR, in which case the appropriate behavior would seem to be to call close again with the same argument. Since this code was written by someone with far more experience than I in both C and UNIX, and additionally has stood unchanged in qmail for over a decade, I assume there must be some nuance that I'm missing that makes this code correct. Can anyone explain that nuance to me?

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• cx_Oracle makes subprocess give OSError

  - by Shrikant Sharat

  I am trying to use the cx_Oracle module with python 2.6.6 on ubuntu Maverick, with Oracle 11gR2 Enterprise edition. I am able to connect to my oracle db just fine, but once I do that, the subprocess module does not work anymore. Here is an iPython session that reproduces the problem... In [1]: import subprocess as sp, cx_Oracle as dbh In [2]: sp.call(['whoami']) sharat Out[2]: 0 In [3]: con = dbh.connect('system', 'password') In [4]: con.close() In [5]: sp.call(['whomai']) --------------------------------------------------------------------------- OSError Traceback (most recent call last) /home/sharat/desk/calypso-launcher/<ipython console> in <module>() /usr/lib/python2.6/subprocess.pyc in call(*popenargs, **kwargs) 468 retcode = call(["ls", "-l"]) 469 """ --> 470 return Popen(*popenargs, **kwargs).wait() 471 472 /usr/lib/python2.6/subprocess.pyc in __init__(self, args, bufsize, executable, stdin, stdout, stderr, preexec_fn, close_fds, shell, cwd, env, universal_newlines, startupinfo, creationflags) 621 p2cread, p2cwrite, 622 c2pread, c2pwrite, --> 623 errread, errwrite) 624 625 if mswindows: /usr/lib/python2.6/subprocess.pyc in _execute_child(self, args, executable, preexec_fn, close_fds, cwd, env, universal_newlines, startupinfo, creationflags, shell, p2cread, p2cwrite, c2pread, c2pwrite, errread, errwrite) 1134 1135 if data != "": -> 1136 _eintr_retry_call(os.waitpid, self.pid, 0) 1137 child_exception = pickle.loads(data) 1138 for fd in (p2cwrite, c2pread, errread): /usr/lib/python2.6/subprocess.pyc in _eintr_retry_call(func, *args) 453 while True: 454 try: --> 455 return func(*args) 456 except OSError, e: 457 if e.errno == errno.EINTR: OSError: [Errno 10] No child processes So, the call to sp.call works fine before connecting to oracle, but breaks after that. Even if I have closed the connection to the database. Looking around, I found http://bugs.python.org/issue1731717 as somewhat related to this issue, but I am not dealing with threads here. I don't know if cx_Oracle is. Moreover, the above issue mentions that adding a time.sleep(1) fixes it, but it didn't help me. Any help appreciated. Thanks.

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• select always returns -1 while trying to read from socket and stdin

  - by Aleyna

  Hello I have the following code implemented on C++(Linux) to check on my listening socket and stdin using select. select however keeps returning -1 no matter what I try to do! What's wrong with that code :s I will appreciate any help. Thanks highsock = m_sock; //listening socket memset((char *) &connectlist, 0, sizeof(connectlist)); memset((char *) &socks, 0, sizeof(socks)); int readsocks; struct timeval timeout; timeout.tv_sec = 60; timeout.tv_usec = 0; while (1) { updateSelectList(); //cout << "highest sock: " << highsock << endl; tempreadset = readset; readsocks = select(highsock+1, &tempreadset, NULL, NULL, &timeout); //cout << "# ready: " << readsocks << endl; if (readsocks < 0) { if (errno == EINTR) continue; cout << "select error" << endl; } if (readsocks > 0) { readFromSocks(); } } void readFromSocks() { if (FD_ISSET(STDIN, &readset)) { ... } else if (FD_ISSET(m_sock, &readset)) { ... } } void updateSelectList() { FD_ZERO(&readset); FD_SET(STDIN, &readset); FD_SET(m_sock, &readset); for (int i=0; i<MAXCONNECTIONS; i++) { if (connectlist[i] != 0) { FD_SET(connectlist[i], &readset); if (connectlist[i] > highsock) highsock = connectlist[i]; } } highsock = max(max(m_sock, STDIN), highsock); }

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• How to interrupt a thread performing a blocking socket connect?

  - by Jason R

  I have some code that spawns a pthread that attempts to maintain a socket connection to a remote host. If the connection is ever lost, it attempts to reconnect using a blocking connect() call on its socket. Since the code runs in a separate thread, I don't really care about the fact that it uses the synchronous socket API. That is, until it comes time for my application to exit. I would like to perform some semblance of an orderly shutdown, so I use thread synchronization primitives to wake up the thread and signal for it to exit, then perform a pthread_join() on the thread to wait for it to complete. This works great, unless the thread is in the middle of a connect() call when I command the shutdown. In that case, I have to wait for the connect to time out, which could be a long time. This makes the application appear to take a long time to shut down. What I would like to do is to interrupt the call to connect() in some way. After the call returns, the thread will notice my exit signal and shut down cleanly. Since connect() is a system call, I thought that I might be able to intentionally interrupt it using a signal (thus making the call return EINTR), but I'm not sure if this is a robust method in a POSIX threads environment. Does anyone have any recommendations on how to do this, either using signals or via some other method? As a note, the connect() call is down in some library code that I cannot modify, so changing to a non-blocking socket is not an option.

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• AIX specific socket programming query

  - by kumar_m_kiran

  Hi All, Question 1 From SUSE man pages, I get the below details for socket connect options If the initiating socket is connection-mode, then connect() shall attempt to establish a connection to the address specified by the address argument. If the connection cannot be established immediately and O_NONBLOCK is not set for the file descriptor for the socket, connect() shall block for up to an unspecified timeout interval until the connection is established. If the timeout interval expires before the connection is established, connect() shall fail and the connection attempt shall be aborted. If connect() is interrupted by a signal that is caught while blocked waiting to establish a connection, connect() shall fail and set errno to [EINTR], but the connection request shall not be aborted, and the connection shall be established asynchronously. Question : Is the above contents valid for AIX OS (especially the connection time-out, timed wait ...etc)?Because I do not see it in AIX man pages (5.1 and 5.3) Question 2 I have a client socket whose attributes are a. SO_RCVTIMEO ,SO_SNDTIMEO are set for 5 seconds. b. AF_INET and SOCK_STREAM. c. SO_LINGER with linger on and time is 5 seconds. d. SO_REUSEADDR is set. Note that the client socket is not O_NONBLOCK. Question : Now since O_NONBLOCK is not set and SO_RCVTIMEO and SO_SNDTIMEO is set for 5 seconds, does it mean a. connect in NON Blocking or Blocking? b. If blocking, is it timed blocking or "infinite" time blocking? c. If it is infinite, How do I establish a "connect" system call which is O_BLOCKING with timeout to t secs. Sorry if the questions are be very naive. Thanks in advance for your input.

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• kernel get stack when signalled

  - by yoavstr

  hi there i write readers and writers where the kernel have to syncronize between them and block writer who already read a massage when i am in the queue waiting I get signal so I do the fallowing while (i_Allready_Read(myf) == ALLREADY_READ || isExistWriter == false ) //while (!(i_Allready_Read(aliveProc,current->pid))) { int i, is_sig = 0; printk(KERN_INFO "\n\n*****entered set in read ******\n\n" ); if (i_Allready_Read(myf) == ALLREADY_READ ) wait_event_interruptible (readWaitQ1, !i_Allready_Read(myf)); else wait_event_interruptible (readWaitQ1, isExistWriter); //printk(KERN_INFO "Read Wakeup %d\n",current->pid); for (i = 0; i < _NSIG_WORDS && !is_sig; i++) { is_sig = current->pending.signal.sig[i] & ~current->blocked.sig[i]; } if (is_sig) { handledClose(myf); module_put (THIS_MODULE); return -EINTR; } } return 0;//success } inline void handledClose(struct file *myf)//v { /* *if we close the writer other writer *would be able to enter to permissiones */ if (myf == writerpid ) { isExistWriter = DOESNT_EXIST; //printk(KERN_INFO "procfs_close : this is pid that just closed %d \n", writerpid); } /* *else its a reader so our numofreaders *need to decremented */ else { removeFromArr(myf); numOfReaders--; } } and my close does nothing ... what did i do wrong?

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